Recently, there is known a catnap condition detecting apparatus that determines an opened/closed condition of an eye of a driver based on an image of the face of the driver of a vehicle in order to detect a catnap condition of the driver.
For example, patent literature 1 discloses a catnap condition detecting apparatus that detects a catnap condition of a driver in accordance with a change in a light environment and a difference in the position of the face originating from individual difference of the driver. The catnap condition detecting apparatus disclosed in patent literature 1 detects the open level of an eye from the maximum continuous number of labeled regions included in an eye region in the vertical direction when determining opening/closing of the eye, thereby determining whether or not the eye is opened or closed.
Moreover, patent literature 2 discloses an eye condition detecting apparatus which estimates a situation in which a driver feels brightness, and which corrects an opened/closed eye determination reference, thereby improving the detection precision. The eye condition detecting apparatus disclosed in patent literature 2 learns the maximum value of the open level of the eye and the minimum value thereof from a change in the open level values of the eye in time series output plural times from an eye-open-level detecting circuit, and sets an opened/closed eye determination reference. The eye condition detecting apparatus disclosed in patent literature 2 slightly corrects the opened/closed eye determination reference when determining that the driver feels brightness. Hence, false determination as the eye being closed can be suppressed when the driver has a narrowed eye because of brightness.
Furthermore, patent literature 3 discloses a sleepiness determining apparatus that can determine a sleepiness condition. The sleepiness determining apparatus disclosed in patent literature 3 calculates an open level of an eye based on images of an eye region, obtains a weighting factor relative to the calculated eye open level based on a sigmoidal function, and multiplies the weighting factor by the eye open level, thereby calculating a weighted eye open level. The sleepiness determining apparatus disclosed in patent literature 3 compares the accumulated value of the weighted eye open levels with first and second threshold values both set beforehand, thereby determining a sleepiness level. According to the sleepiness determining apparatus disclosed in patent literature 3, because the eye open level is weighted and accumulated, the sleepiness condition of a driver can be determined in consideration of the contribution of sleepiness with respect to a condition in which the driver opens his/her eyes by half.
Still further, patent literature 4 discloses an eye condition detecting apparatus comprising reference correcting means for learning an opened/closed eye determination reference again when it is detected that a driver just starts driving and the open level of an eye changes. The eye condition detecting apparatus disclosed in patent literature 4 learns the opened/closed eye determination reference again at an appropriate timing in accordance with a situation. For example, when determining that the driver feels brightness because of a change in a light environment, the eye condition detecting apparatus does not learn the opened/closed eye determination reference again. Accordingly, it is possible for the eye condition detecting apparatus to prevent the opened/closed eye determination reference from becoming excessively small, and to avoid determining that the eye is always opened in a condition in which the driver does not feel brightness.